This invention relates in general to pin tumbler locks and deals more particularly with improvements in locks of a type wherein pin tumblers reciprocally positioned by bits cut on one edge of a key release a plug for rotation relative to a supporting cylinder shell.
Heretofore, locks have been provided wherein pin tumblers carried by a key plug are positioned by a properly bitted key reciprocally to clear a shear line between the key plug and its supporting shell and also positioned rotationally to release another locking member so that it also clears the shear line. Typical lock cylinders of the aforedescribed general type are illustrated and described in U.S. Pat. Nos. 3,499,302 and 3,722,240 to Spain et al.; 3,449,303 to Spain; and 3,837,197 to Lopez. Each of the key operated lock cylinders disclosed in the aforesaid prior art references includes pin tumblers reciprocally positioned to clear a shear line and rotationally or angularly positioned to release another locking member which comprises a side bar or fence. While such locks provide a high degree of security and facilitate a large number of possible key changes, utilization of multiple locking elements; e.g. both pin tumblers and a side bar or fence, substantially increase the number of parts and operations required to make a lock, as compared to a lock of conventional pin tumbler type, which utilizes only one form of locking element.
Accordingly, it is the general aim of the present invention to provide improved pin tumbler locks having locking members consisting solely of pin tumbler assemblies, difficult if not impossible to pick, and which provide a significantly greater number of key change possibilities than pin tumbler locks heretofore available. A further aim of the invention is to provide improved pin tumbler locks which may be readily adapted for use in master keyed systems.